Hemolytic uremic syndrome (HUS), a systemic complication of Shiga toxin-producing Escherichia coli (STEC) infection in human beings, is the number one cause of renal failure in children in the United States. Currently, there is no accurate way to predict which children will develop HUS, and there are no proven effective therapies for the disorder once it is diagnosed. Shiga toxin (Stx) binds human neutrophils, and neutrophil-bound Stx has been detected in the blood of children with HUS. Stx also can induce TNF-alpha and IL-1beta production in vitro, and pro-inflammatory cytokines are elevated in children with HUS. Moreover, several studies in animal models have suggested that modulating the immune response can affect the development of clinical disease. Based on this evidence, potential therapies designed to suppress production of pro-inflammatory cytokines during HUS should be explored; however, the details of the pathogenesis of HUS remain elusive, specifically, to what extent circulating Stx contributes to these cytokine alterations in vivo. The edema disease model offers the unique opportunity to assess the contribution of circulating, cell-bound Stx to production of the cytokines IL-10, TNF-alpha and IL-1beta in a naturally- occurring STEC infection. During edema disease, circulating Stx is detected only when bound to erythrocytes, and erythrocyte-bound Stx is strongly associated with development of clinical disease. It is our hypothesis that circulating, cell-bound Stx induces the cytokine alterations that contribute to clinical disease. The work in this proposal will: 1) quantify and define the contribution of varying the amount of cell-bound Stx to clinical disease; 2) identify the relationship between circulating cell-bound Stx and cytokine production; 3) isolate the effects of Stx on cytokine production through the use of an isogenic stx deletion mutant of our STEC strain. Results of this work will: 1) determine the contribution of circulating, cell-bound Stx to both cytokine production and clinical disease; 2) identify additional avenues for potential therapeutic intervention in the prevention of HUS; 3) further our understanding of STEC disease pathogenesis. [unreadable] [unreadable] [unreadable] [unreadable]